The present invention relates to an apparatus and method of controlling ignition timing in an engine with a variably operated intake valve.
There have been proposed apparatuses for controlling intake and exhaust valves using a variably operated valve actuator, for instance, an electromagnetically operated valve actuators. The apparatuses of such the kind are disclosed in Japanese Patent Applications First Publications Nos. 8-200025 and 10-37727.
In addition, recently, there has been developed unthrottled engine operation in which an intake air amount is regulated without actuation of a throttle valve by operating an intake valve at an early closing timing at an engine intake stroke, for the purpose of reduction in engine pumping loss and, therefore, improvement in fuel economy. In this case, the throttle valve is omitted or suplementally disposed within an intake air passage in order to produce a slight negative pressure therewithin.
However, in some engine operating conditions, it is desirable to control the intake air amount by fixing the closing timing of the intake valve to near bottom dead center (BDC) at the engine intake stroke and varying a throttle position corresponding to an opening degree of the throttle valve. Therefore, there is a demand to conduct the intake air amount control by separately controlling the intake valve and the throttle valve.
Assuming that the intake air amount is controlled by variably controlling the intake valve in the separate controls of the intake valve and the throttle valve, the closing timing of the intake valve becomes early, i.e., advanced to reduce the opening duration in order to lessen the intake air amount at low load. This prevents a flow rate of the intake air at an intake port from sufficiently increasing, to thereby attenuate a gas flow within the engine cylinder. Further, the temperature of an air-fuel mixture within the engine cylinder is decreased due to adiabatic expansion caused after the early closure of the intake valve. This causes combustion speed of the air-fuel mixture to be lower than combustion speed thereof in the case of controlling the throttle valve. In addition, there is a difference between the negative pressures within the intake air passage which are generated upon the respective controls of the intake valve and the throttle valve. The negative pressure difference also greatly influences the combustion speed of the air-fuel mixture.
Therefore, if the same ignition timings are used in the different intake control modes in which the intake air amounts are controlled by the separate controls of the intake valve and the throttle valve, there will occur considerable influence on drivability and fuel economy.
It is an object of the present invention to provide a system and method of optimally controlling ignition timing in an engine conditioned in different intake control modes, to thereby improve in performance such as drivability and fuel economy.
According to one aspect of the present invention, there is provided a system for controlling ignition timing in an engine, the system comprising:
an intake valve operative at variable opening and closing timing to regulate an amount of intake air passing therethrough;
a throttle valve operative to variably move between throttle positions to regulate an amount of intake air passing therethrough;
an unthrottled operation control in communication with the intake valve and the throttle valve, the unthrottled operation control performing a first intake control mode in which an intake air amount is controlled by varying. the closing timing of the intake valve, and generating a first mode output indicative of the first intake control mode and providing a control output indicative of the varied closing timing to the intake valve;
a throttled operation control in communication with the intake valve and the throttle valve, the throttled operation control performing a second intake control mode in which the intake air amount is controlled by varying the throttle position of the throttle valve, and generating a second mode output indicative of the second intake control mode and providing a control output indicative of the varied throttle position to the throttle valve; and
an ignition timing control in communication with the unthrottled operation and throttled operation controls, the ignition timing control being operative to determine a first ignition timing in response to the first mode output and determine a second ignition timing different from the first ignition timing in response to the second mode output.
According to a further aspect of the present invention, there is provided a method of controlling ignition timing in an engine having a variably operated intake valve cooperating with a variably operated throttle valve, the method comprising:
determining an engine operating condition;
depending on the engine operating condition determined, selectively conducting one of an unthrottled operation control in which an intake air amount is controlled by varying a closing timing of the intake valve, and a throttled operation control in which the intake air amount is controlled by varying the throttle position of the throttle valve; and
determining an ignition timing to be used in the conducted one of the unthrottled operation and throttled operation controls, the ignition timing comprising first and second ignition timings different from each other.
According to a still further aspect of the present invention, there is provided a computer readable storage device having stored therein data representing instructions executable by a computer to control an engine having a variably operated intake valve cooperating with a variably operated throttle valve, the computer readable storage device comprising:
instructions for determining an engine operating condition;
instructions for depending on the engine operating condition determined, selectively conducting one of an unthrottled operation control in which an intake air amount is controlled by fixing-a throttle position of the throttle valve to a predetermined throttle position and varying a closing timing of the intake valve, and a throttled operation control in which the intake air amount is controlled by fixing the closing timing of the intake valve to a predetermined closing timing and varying the throttle position of the throttle valve; and
instructions for determining an ignition timing to be used in the conducted one of the unthrottled operation and throttled operation controls, the ignition timing comprising first and second ignition timings different from each other.